Delta-sigma modulation is an example of a technique of generating a 1-bit pulse train representing an analog waveform (refer to Non-Patent Literature 1).
Delta-sigma modulation is a kind of oversampling modulation. A delta-sigma modulator is configured to include a loop filter and a quantizer. The quantizer can output a 1-bit pulse train as a quantized signal.
The 1-bit pulse train output from the delta-sigma modulator is restored to the original analog waveform by simply being passed through an analog filter. In other words, the 1-bit pulse train output from the delta-sigma modulator is a digital signal, but represents an analog waveform, and therefore, has properties of both a digital signal and an analog signal.